Because Shiseido is a leading beauty brand based in Asia, the top cosmetics market in the world, and they want a huge celebrity name to promote their company for further success. As Gaga is the biggest Western celebrity in Japan, it makes perfect sense. That is, if you use logic, but you don't seem to be familiar with logic when it concerns Gaga.

Exactly.

I love this look! what is shiseido? is it a japanese car company or something? she is the queen of Japan along with Taylor and Ariana

sweet jesus....

Because Japan stans for her(?)

omg teach ha

I really don't like this outfit

Because she is the definition of a modern icon?

The biggest cosmetics/beauty brand in Asia and one of the biggest in the world.

Landing a Shiseido campaign would be like an American celebrity landing a Lancome campaign. It's the best of the best, the richest of the richest. It's not like a simple Covergirl campaign.